Compressed air supply system and pneumatic system

ABSTRACT

The invention relates to a compressed air supply system ( 11, 21, 22, 23, 24, 25, 30, 41 ) for operating a pneumatic system ( 90, 901, 902 ), in particular a pneumatic suspension of a vehicle, comprising: a compressed air supply ( 1 ); a first pneumatic connection between the compressed air supply ( 1 ) and the pneumatic system ( 90, 901, 902 ), comprising an air desiccator ( 61 ), throttle means ( 62 ) and at least one controllable separation valve ( 63, 63′, 63″, 63′″, 63 IV,  163 ); a second pneumatic connection which is pneumatically connected to the first pneumatic connection and to a ventilation connection ( 3 ) for connecting to the surroundings and which has at least one controllable ventilation valve ( 73, 73′, 73″, 73′″, 73   IV   , 173 ). According to the invention, said at least one controllable separation valve ( 63, 63′, 63″, 63′″, 63   IV   , 163 ) and the throttle means ( 62 ) are aligned in the first pneumatic connection in such a manner that the at least one controllable separation valve ( 63, 63′, 63″, 63′″, 63   IV   , 163 ) can be switched in an open state, into the flow through mode, and in the closed state, into a separation mode. In the closed state, the first pneumatic connection is completely closed in both directions and said at least one controllable separation valve ( 63, 63′, 63″, 63′″, 63   IV   , 163 ) can be switched, in the flow through mode, between a first control state, associated with a closed state, and a second control state which is associated with an open state.

The invention generally relates to a compressed air supply installation in accordance with the preamble of claim 1. The invention furthermore relates to a pneumatic system in accordance with the preamble of claim 14 having a compressed air supply installation of this kind. The invention furthermore relates to a method for operating the compressed air supply installation in accordance with the preamble of claim 15.

A compressed air supply installation is used in vehicles of all kinds, in particular for supplying an air spring installation on a vehicle with compressed air. Air spring installations can also comprise leveling devices, by means of which the distance between the vehicle axle and the vehicle body can be adjusted. An air spring installation of a pneumatic system can comprise a number of pneumatic bellows connected pneumatically to a common line (gallery), which can raise the vehicle body as they are filled to an increasing extent and, correspondingly, can lower the vehicle body as the filling decreases. As the distance between the vehicle axle and the vehicle body or ground clearance increases, spring travels become longer and it is possible to cope even with relatively large irregularities in the ground without the occurrence of contact with the vehicle body. Such systems are increasingly being used in all-terrain vehicles and sport utility vehicles (SUV). Particularly with SUVs, it is desirable, in the case of very powerful engines, that the vehicle should, on the one hand, be provided with a relatively small ground clearance for high speeds on the road and, on the other hand, with a relatively large ground clearance for off-road use. It is furthermore desirable to implement a change in the ground clearance as quickly as possible, and this increases the demands in respect of the rapidity, flexibility and reliability of a compressed air supply installation.

In order to ensure long-term operation of the compressed air supply installation, a main pneumatic line has an air drier, by means of which the compressed air can be dried. This avoids accumulation of moisture in the pneumatic system. At relatively low temperatures, moisture can lead to the formation of crystals that damage valves and can also lead to unwanted faults in the compressed air supply installation and in the pneumatic installation. An air drier has a desiccant, generally in the form of a granular fill, through which the compressed air can flow, allowing the granular fill to take up moisture contained in the compressed air by adsorption. If appropriate, an air drier can be designed as a regenerative air drier. This can be accomplished by arranging for the dried compressed air from the pneumatic installation, in particular an air spring installation, to flow through the granular fill in a countercurrent or co-current pattern relative to the filling direction during each venting cycle. Regeneration of the air drier is made possible essentially by a pressure swing at the air drier, with a pressure prevailing during regeneration generally being lower in comparison with adsorption in order to enable moisture to be released from the granules. For this purpose, the vent valve arrangement can be opened, with the regeneration capacity of the air drier generally being dependent on the pressure conditions and the pressure swing in the compressed air supply installation. For a “pressure swing adsorption process” of this kind, too, it has proven desirable to make a compressed air supply installation flexible and, at the same time, reliable. In particular, the aim is, on the one hand, to allow relatively quick venting and yet to make available an air pressure sufficiently low for regeneration of the air drier.

DE 35 42 974 A1 of the applicant has disclosed a leveling device for vehicles which is provided with air filters and by means of which a predetermined distance between the vehicle cell and the vehicle axle can be adjusted in accordance with the vehicle loading by filling or emptying the air springs. The device has a safety valve that can be controlled by means of the pressure in the air springs. In an installation of this kind, the air drier can be regenerated via a restrictor and a nonreturn valve that opens counter to a filling direction.

DE 199 11 933 B4 discloses a compressed air supply installation having an air drier with a first compressed air supply line, wherein the compressed air is passed through a desiccant in the air drier, and with a second compressed air supply line, through which there can be a flow without the compressed air being passed through the desiccant.

Many different approaches to the design of a first pneumatic connection between a compressed air feed mentioned at the outset and a pneumatic installation mentioned at the outset are known from the prior art. These allow for the basic functions of a compressed air supply installation when supplying air to the pneumatic installation and releasing air from the pneumatic installation. With respect to the abovementioned requirement for relatively quick venting with an air pressure that is nevertheless sufficiently low for regeneration of the air drier, these approaches are still in need of improvement, however.

DE 102 23 405 B4 discloses an air spring system on a motor vehicle with a compressed air supply installation having a delivery line for connecting a compressor to the air springs and a vent line, via which the delivery line can be connected to atmosphere while being capable of being shut off by means of a switching valve. A segment of the delivery line in which a restrictor is arranged in parallel with a nonreturn valve and in parallel with a further switching valve, said segment being designed as a pneumatic parallel circuit, is provided between a drier and level control valves in a gallery of the air spring installation. The switching valve in the vent line and the switching valve in the segment of the delivery line are connected to the same output stage of a control unit by electric control lines.

DE 101 21 582 C2 discloses an air supply unit for an air suspension installation, in which a vent valve in a vent line, an air spring valve in the gallery of the air suspension installation and an air control valve are provided. All three valves are connected to an electronic control unit. The air control valve is connected in parallel with a nonreturn valve in a segment of a delivery line between a drier and a spring valve, said segment being designed as a pneumatic parallel circuit, with the result that, although air can be taken into the air spring installation unhindered, it can only be released again in a controlled manner via the air control valve. To release compressed air from the air suspension installation, all three of the valves mentioned above are opened.

U.S. Pat. No. 6,098,967 discloses a compressed air supply installation of the type stated at the outset, in which a segment designed as a pneumatic parallel circuit and containing two branch lines connected in parallel is arranged in the main pneumatic line between the air drier and the air spring installation, wherein, in a first branch line, a nonreturn valve, through which there can be a flow for flow admission, and, in a second branch line, a nonreturn valve, through which there can be a flow for venting, are connected in series with a restrictor and a switching valve.

EP 1 216 860 B1 discloses a leveling installation for a motor vehicle, having air springs and having a control unit which exercises open-loop or closed-loop control over the functions of filling and emptying in accordance with the level of the vehicle body. Among the elements connected to the control unit are a controllable directional control valve of a compressed air supply installation and a controllable directional control valve arranged ahead of a reservoir. The controllable directional control valve of the compressed air supply installation, which is subject only to fixed restriction in the open state, is arranged in parallel with a nonreturn valve.

The need for further improvement in the connection of an air spring installation to the compressed air supply installation, the relatively complex nature of said connection and the large number of components involved in it are problematic in all of the compressed air supply installations mentioned. Owing to the fact that the abovementioned segment is generally designed as a parallel circuit in a main pneumatic line, said line is open, at least in a bypass line, or has to be opened against a counterpressure, e.g. that of a nonreturn valve.

In FIG. 9, EP 1 243 447 A2 discloses a closed leveling installation having a gallery line, to which a number of bellows, each serving as a pressure chamber for an air spring, and a controllable isolating valve arrangement of a pneumatic installation are connected, said arrangement being formed by a first 2/2-way valve and a second 2/2-way valve arranged in series. The second directional control valve is arranged in the compressed air line between the first controllable directional control valve and the air springs. The gallery line is connected to the second directional control valve. The pneumatic installation can be filled and emptied from the compressed air supply installation, which is connected to the first directional control valve, via the isolating valve arrangement on one side of a drier. A compressed air reservoir is connected to the compressed air supply installation via a separate directional control valve and a separate pneumatic line on the other side of the drier.

EP 1 380 453 B1 discloses a similarly closed leveling installation for vehicles, by means of which a vehicle body is sprung relative to at least one vehicle axle. The pneumatic installation can be filled and emptied from the compressed air supply installation on one side of a drier, said installation being connected to a single 2/2-way valve. In this installation, a compressed air reservoir is likewise connected to the compressed air supply installation via a separate directional control valve and a separate pneumatic line on the other side of the drier. The compressed air reservoir is isolated from the compressed air supply installation independently of an air spring installation, by means of a 4/4-way valve or two 2/2-way valves.

These pneumatic systems too, in which the connection of the pneumatic installation to the necessarily closed compressed air supply installation is relatively complex, are still capable of improvement.

This is the starting point of the invention, the object of which is to indicate a compressed air supply installation for operating a pneumatic installation which is an improvement over the prior art and, in particular, operates reliably and yet flexibly and, if required, quickly. The aim is, in particular, a compressed air supply installation which is of relatively simple construction and yet, on the one hand, allows relatively quick venting combined with drier regeneration in a manner which is as advantageous as possible. Another particular aim is improved acoustics in the compressed air supply installation. It is likewise an object of the invention to indicate a pneumatic system of advantageous design and a method employing the compressed air supply installation.

in respect of the compressed air supply installation, the object is achieved by the invention with a compressed air supply installation of the type stated at the outset in which, according to the invention, the features of the characterizing part of claim 1 are provided.

The invention presents a pneumatic system in claim 14 and a method in claim 15 employing a compressed air supply installation according to the invention.

A compressed air supply installation is operated with compressed air, e.g. within a pressure level range of from 5 to 20 bar, in a pneumatic system having a pneumatic installation, e.g. an air spring installation described above, wherein the compressed air of the compressed air supply installation is made available from a compressed air feed. The compressed air for the compressed air feed can be produced, in particular, by an air compressor arranged between an air feed and a compressed air port. To supply the pneumatic installation, the compressed air feed is connected to the compressed air port leading to the pneumatic installation by a first pneumatic connection. The first pneumatic connection of the compressed air supply installation mentioned at the outset advantageously has a main pneumatic line. Moreover the compressed air supply installation of the type stated at the outset has a second pneumatic connection, advantageously a vent line, having a controllable vent valve, which pneumatic connection is connected pneumatically to the main pneumatic line and to a vent port leading to the environment. The compressed air feed is thereby connected pneumatically, inter alia via the controllable vent valve, to a vent port leading to the environment. By means of the controllable vent valve, the compressed air supply installation can be vented by discharging air toward the vent port in order, in particular, to vent the pneumatic installation.

The invention starts from the consideration that, in principle, an advantageous design of the pneumatic connection between the compressed air feed and a compressed air port leading to the pneumatic installation can be a basis for improved drier regeneration and, in particular, also for flexible and, if required, quick venting of the compressed air supply installation and/or of the pneumatic installation or for the admission of air thereto. In a development, the invention starts from the consideration that a main pneumatic line for the formation of the pneumatic connection can be of relatively simple design for this purpose. The invention has recognized that this requires the pneumatic connection to be designed in such a way that it can be closed bidirectionally and completely. For this purpose, the invention makes provision for the controllable isolating valve and restricting means to form a series arrangement in the main pneumatic line.

It is advantageous if the isolating valve and/or the vent valve are directional control valves. In an isolating mode, the controllable isolating valve, in particular in the form of a directional control valve, can be switched to a closed state, with the pneumatic connection being bidirectionally and completely cut off, i.e. closed, in the closed state. In other words, a pneumatic connection between the compressed air feed and the compressed air port leading to the pneumatic system can be closed in an airtight manner or is closed in an airtight manner when the controllable isolating valve is in the closed state. This leads to an advantageous decoupling of the compressed air supply installation and the pneumatic installation. It is advantageous if the main pneumatic line, if appropriate together with a further pneumatic line in series, is the only line of the pneumatic connection, at least between an air drier of the compressed air supply installation and a gallery line of a pneumatic installation, in particular for the formation of the pneumatic system according to the invention.

In the case of a pneumatic connection which can be cut off bidirectionally and completely, it is advantageously possible to implement a very wide range of operating states in the pneumatic installation, in particular an air spring installation, without thereby affecting the compressed air supply installation—in particular, a possibly ineffective action on the air drier is thereby avoided. For this purpose, it is advantageous if the main pneumatic line is provided as a single line no as to form the pneumatic connection between the compressed air feed and the compressed air port. Thus, in the case of a pneumatic connection that is completely and bidirectionally closed pneumatically, a pressure measurement can advantageously be performed in the reservoir or the bellows in an air spring installation connected to the compressed air port. In particular, it has also been found that a pressure measurement that would otherwise take a relatively long time—either due to relatively complex circuits or ineffective action on the drier—can be performed relatively quickly. It is also possible to cross-connect the reservoir and/or the bellows via the gallery of the air spring installation without impairing the compressed air supply installation, in particular an air drier.

Conversely, the present concept of an invention offers the possibility of adjusting the controllable isolating valve in such a way in an open state—in a through-flow mode—that the series arrangement consisting of the controllable isolating valve in the open state and the restricting means forms a series arrangement which is optimized for the filling of the pneumatic installation and the venting of the pneumatic installation and in which drier regeneration and the requirements for a compressed air supply installation that can be actuated flexibly and, if required, quickly are also accomplished.

According to the invention, this can be implemented in a particularly effective manner if the controllable isolating valve and the controllable vent valve are set up to be controlled by means of a control signal common to both. In particular, both valves are connected to an electronic controller by means of a control line common to both. Thus, control signals can be transmitted from an electronic controller, in particular a common electronic controller, in a control line common to both.

In particular, it has proven advantageous if the controllable isolating valve is formed with a first coil and the controllable vent valve is formed with a second coil, wherein the first coil and the second coil are formed with a single coil former common to both coils. The coil can preferably be formed with a first coil armature, which is arranged in the coil former and has a first valve body, and with a second coil armature, which is arranged in the coil former and has a second valve body. A directional control valve, which is also referred to as a double armature solenoid valve in a special design, can thus embody both the isolating valve and the vent valve in a very compact design.

If required, it is also possible, in principle, for the controllable isolating valve to be formed with a first coil and for the controllable vent valve to be formed with a second coil, wherein the first and the second coil have separate coil formers, and yet for the controllable isolating valve and the controllable vent valve to be set up to be controlled by means of a control signal common to both.

In principle, the at least one controllable isolating valve can be arranged at any point in the first pneumatic connection between the compressed air feed and the pneumatic installation.

In the context of a first particularly preferred development, the main pneumatic line of the pneumatic connection runs between the compressed airfeed and a compressed air port leading to the pneumatic installation. This has the advantageous effect that the at least one isolating valve can be arranged within a compressed air supply installation that can be configured as a unit. It is advantageous that, in a closed state of the controllable isolating valve, the main pneumatic line between the air drier and the compressed air port is bidirectionally and completely closed.

In the context of a second particularly preferred development, the main pneumatic line runs between the compressed air feed and a gallery port and/or a reservoir port in the pneumatic installation. This has the advantageous effect that the at least one controllable isolating valve can also be provided in a pneumatic installation, i.e. outside a compressed air supply installation that can be configured as a unit. It is advantageous that, in a closed state of the controllable isolating valve, the main pneumatic line between the air drier and the gallery port and/or a reservoir port in the pneumatic installation is bidirectionally and completely closed.

In particular, it has proven advantageous to provide a first controllable isolating valve and a second controllable isolating valve. The concept of the invention is thus not restricted to a single controllable isolating valve. On the contrary, it has proven advantageous, in the context of the second preferred embodiment explained above, that the first controllable isolating valve should be formed with a first coil and the second controllable isolating valve should be formed with a second coil. In a particularly preferred development, the first coil and the second coil can be formed with a single coil former common to both coils. In this case, the first controllable isolating valve and the second controllable isolating valve can be implemented as part of a “double solenoid valve arrangement”, wherein at least one, preferably the first and the second, controllable isolating valve of the double solenoid valve arrangement is/are controllable in accordance with the concept of the invention.

The preferred developments in respect of a compressed air supply installation which are described below can be implemented for the at least one controllable isolating valve, which is arranged within a compressed air supply installation that can be configured as a unit. The developments can also be implemented in relation to at least one controllable isolating valve arranged separately from a unit of the compressed air supply installation, e.g. a controllable isolating valve in the pneumatic installation, in particular in a valve block thereof.

Advantageous developments of the invention—in particular also of the pneumatic system and of the method—can be found in the dependent claims and, in particular, indicate advantageous possibilities for implementing the above-explained concept in the context of the object stated and in respect of other advantages.

According to the invention, at least the controllable isolating valve can be switched over between a first control state and a second control state. In this case, the first control state is assigned to a closed state of the controllable isolating valve, and the second control state is assigned to an open state of the controllable isolating valve. The first and/or second control state can advantageously be specified at least to the controllable isolating valve by means of an electronic controller, being specified to the controllable isolating valve, for example, by means of a suitable control signal passed via a control line. The first control state can be made such that the isolating valve moves completely to the closed state. The first control state can also be configured in such away that the isolating valve begins to move to the closed state at the beginning of the switching operation without reaching the closed state. It is likewise possible for the second control state to move the controllable isolating valve into the completely open state. The second control state can also be made such that the controllable isolating valve opens partially at the beginning of the switching operation and then continues to move toward the completely open state without reaching the completely open state. For example, the first and the second control state can be made such that the controllable isolating valve moves backward and forward dynamically between a completely closed state and a completely open state without the controllable isolating valve being completely closed or completely open.

Owing to the series arrangement according to the invention of the isolating valve and the restricting means, the main pneumatic line is designed to be actuated in a relatively simple, flexible and yet reliable manner. As a particularly preferred option, a through-flow quantity at least for the controllable isolating valve, that is to say, if appropriate, also for the controllable vent valve, can be subjected to closed-loop and/or open-loop control in the through-flow mode. In the context of the abovementioned development, the invention has recognized that the controllable isolating valve can be controlled in such a way that a setting which is advantageous for venting, for air admission and equally for drier regeneration and for the acoustics of the compressed air supply installation is obtained for the series arrangement with the restricting means. In particular, it is possible, in the through-flow mode, for the controllable isolating valve to be subjected to closed-loop and/or open-loop control in respect of a flow rate of a compressed air flow in such a way that an explosive release of air is avoided, even in the case of relatively quick venting operations. There would be a risk of explosive air release in a compressed air supply installation whenever an excessively large volume of compressed air is released at too high a pressure within too short a time.

It has been found that a configuration and matching of first and second control states can advantageously be used to implement an effective nominal width of the series arrangement comprising the restricting means and the controllable isolating valve. Thus, in the context of a particularly advantageous development, it is possible, in the through-flow mode, that at least the controllable isolating valve can be switched over between the first and the second control state in such a way that an effective nominal width of the series arrangement comprising the restricting means and the controllable isolating valve is below an actual nominal width of the restricting means. In the context of this particularly preferred development, it is possible in practice, by means of the series arrangement, to obtain an adjustable electromagnetically controllable restrictor, while nevertheless ensuring that the pneumatic connection can be cut off bidirectionally and completely. In this way, on the one hand, the advantages at which the concept of the invention aims are achieved. In addition, it is advantageously possible to adjust the flow rate for the controllable isolating valve under closed-loop and/or open-loop control in the through-flow mode.

It is particularly advantageous that a flow rate of a compressed air flow can additionally be subjected to open-loop and/or closed-loop control for the controllable vent valve—if appropriate in a manner matched to the state of the controllable isolating valve. In particular, the controllable vent valve can be subjected to closed-loop and/or open-loop control in respect of a flow rate of a compressed air flow in the through-flow mode. To achieve this, the controllable isolating valve and/or the controllable vent valve can preferably be subjected to closed-loop and/or open-loop control in a manner matched to one another. In particular, the controllable isolating valve and/or the controllable vent valve can be connected to a controller. In particular, this is a common electronic controller. In principle, however, two coupled electronic controllers can be provided, being set up in such a way that a control state of the vent valve is matched to a control state of the isolating valve.

The controller can specify a control state of the isolating valve and/or of the vent valve by means of a very wide range of parameters. The parameters can be detected within a sensor system, for example, or can be taken from an ECU or some other vehicle controller or from a heuristic system. It is particularly advantageous if the controllable isolating valve and/or the controllable vent valve can be subjected to closed-loop and/or open-loop control by means of an electronic controller in accordance with an air admission or air release situation. In this context, a state of the drier, in particular a requirement for drier regeneration, is preferably taken into account. It is particularly advantageous if circumstances that affect the acoustics of the compressed air supply installation, in particular possible circumstances that are responsible for an explosive release of air, are taken into account.

State values, such as a gallery pressure, a discharge characteristic of the pneumatic installation, a switching speed of the isolating valve and/or of the vent valve or a value of a difference between the setpoint and the actual value of a compressed air supply installation and/or pneumatic installation can preferably be used.

In principle, a first control state and/or a second control state can be adjusted in a variable manner. This allows a variable time characteristic of a switching operation or of a switching amplitude at least of the controllable isolating valve, for example. Thus, for example, the controllable isolating valve can be capable of being switched over continuously between the first and the second control state. It is also possible, for example, for a switching speed and/or an overall opening time and/or an overall closing time of an isolating valve to be adjusted in an advantageous manner.

In the context of a particularly preferred development, it has proven advantageous that at least the controllable isolating valve can be switched over backward and forward between the first and the second control state at a clock rate of a control state change. In particular, different clock rates of a control state change can be provided. For example, the controllable isolating valve can be switched over backward and forward between the first and the second control state at a first clock rate in a first time segment and can be switched over backward and forward at a second clock rate in a second time segment. It is thus possible by electronic means to obtain one or more effective nominal widths for the series arrangement comprising the restricting means and the controllable isolating valve in accordance with the advantageous development explained above. In principle, a clock rate of a control state change can advantageously be used to set a suitable effective nominal width of the series arrangement. It has been found that a clock rate of between 4 Hz and 20 Hz is particularly suitable for setting an effective nominal width in such a way that a comparative improvement in the acoustics and regeneration capacity of the drier is made available by means of the series arrangement of the compressed air supply installation. In the frequency range indicated, the clock rate of a control state change can realistically be converted into a backward and forward movement of the armature at the clock rate, even given the inert mass of the armature of the controllable isolating valve.

Fundamentally, the term “restricting means” should be taken to mean any means that restricts a line cross section of the main pneumatic line. A preferred nominal width of the main pneumatic line is greater than 4 mm. The restricting means preferably has an actual nominal width, defined by the smallest clear restrictor cross section, of greater than 0.6 mm. Depending on the line cross section of the main pneumatic line, a restrictor cross section can be up to 8 mm. An actual nominal width of the restricting means is preferably between 1 and 3 mm, in particular 2.5 mm. According to the particularly preferred development of the invention explained above, an effective nominal width of the series arrangement comprising the restricting means and the controllable isolating valve is less than the actual nominal width, thus specified, of the restricting means.

As a particularly preferred option, the restricting means is formed as a restrictor separate from the isolating valve. As explained, these can fundamentally be any kind of variation in the line cross section of the main pneumatic line or can be a specially designed restricting device. It is also possible for a restricting means to be formed in the isolating valve and/or in another valve, e.g. by means of an aperture of a valve seat of the isolating valve and/or of the further valve.

It is particularly advantageous if the controllable isolating valve and/or the controllable vent valve are switched over between the first and the second control state by means of a control signal. The control signal is preferably in the form of a pulse width modulated control signal (PWM control signal). A control signal is advantageously in the form of a current and/or voltage signal. A PWM control signal with a suitable frequency and a suitable pulse/no pulse ratio is preferably made available. A frequency of between 5 kHz and 20 kHz and a pulse/no pulse ratio of between 1:100 and 100:1 that can be adjusted in sufficiently fine steps has proven to the particularly preferred. If required, a somewhat coarser pulse/no pulse ratio of between 1:10 and 10:1 may also be sufficient.

According to the above-mentioned development, a first PWM control signal can be assigned to a first control state of an isolating valve and/or of a vent valve and a second PWM control signal can be assigned to a second control state of an isolating valve and/or of a vent valve, for example. By means of a frequency and/or a pulse/no pulse ratio of a clocked control signal, in particular a PWM control signal, an effective nominal width of the series arrangement can advantageously be adjusted.

The controllable isolating valve and/or the controllable vent valve is/are preferably set up to be controlled by means of a control signal common to both. For this purpose, the switching point and the switching states of the isolating valve and/or the vent valve can advantageously be matched to one another. The switching points and the switching amplitudes of the isolating valve and the vent valve can be formed by the control signals and/or by suitably designed valve springs.

In the isolating mode, the controllable isolating valve and the vent valve are preferably closed when deenergized. In particular, it has proven advantageous for the vent valve to move to a through-flow mode only after the isolating valve has switched to the open state. This advantageously makes it possible to avoid an explosive release of air since a partial pressure relief can take place first through the opening of the isolating valve, before the vent valve opens. Thus, the vent valve opens at a relatively low pressure amplitude, this being advantageous for the purpose of reducing an acoustic effect.

In the context of a first particularly preferred variant, the vent valve, as a directly switched valve, is part of a solenoid valve arrangement for directly switching the compressed air volume, wherein the solenoid valve arrangement is free of a control valve. In other words, the solenoid valve arrangement according to this variant is used to obtain a directly controlled solenoid vent valve arrangement. It has been found that direct switching of an overall compressed air volume means that the switching time of the directly controlled solenoid vent valve arrangement can be below that of indirectly controlled solenoid vent valve arrangements; this being the case for vent cross sections of the same size. As is evident from this variant, this has advantages when venting the compressed air supply installation while regenerating the air drier.

In a second particularly preferred developed variant, the vent valve, as an indirectly switched relay valve, is part of a solenoid valve arrangement for indirectly switching a compressed air volume. The solenoid valve arrangement has a control valve for controlling the relay valve, which control valve is subjected to a pressure of the main pneumatic line. In a first preferred modification, the pressure can be a total pressure in the main pneumatic line. In a second modification, the pressure can also be a partial pressure in the main pneumatic line. In other words, the solenoid valve arrangement according to this second variant is used to obtain an indirectly controlled solenoid vent valve arrangement. It has been found that a control pressure can be kept relatively low through indirect switching of an overall compressed air volume. As is evident from the first modification of this second variant, it is nevertheless possible to achieve a relatively quick switching action of the vent valve by using a total pressure in the main pneumatic line.

Illustrative embodiments of the invention will now be described below with reference to the drawing. These are not necessarily intended to show the illustrative embodiments to scale but rather the drawing, where useful for explanatory purposes, is executed in a schematic and/or slightly distorted form. With a view to supplementing the teaching that can be ascertained directly from the drawing, attention is drawn to the relevant prior art. At the same time, it should be taken into account that many different modifications and changes regarding the shape and the details of an embodiment can be made without departing from the general concept of the invention. The features of the invention which are disclosed in the description, in the drawing and in the claims may be essential either individually or in any combination for the development of the invention. Moreover, all combinations comprising at least two of the features disclosed in the description, the drawing and/or the claims fall within the scope of the invention. The general concept of the invention is not restricted to the exact shape or details of the preferred embodiment shown and described below or restricted to subject matter which might be restricted in comparison with the subject matter claimed in the claims. In the case of the dimension ranges stated, the intention is also to disclose as limiting values values which lie within the stated limits and that any such values should be susceptible of being used and claimed. For the sake of simplicity, the same reference signs are used below for identical or similar parts or parts with an identical, or similar function.

Further advantages, features and details of the invention will emerge from the following description of the preferred illustrative embodiments and from the drawing, in which:

FIG. 1 shows a circuit diagram of a pneumatic system with a particularly preferred embodiment of a compressed air supply installation according to a first developed variant, in which the vent valve, as a directly switched valve, is part of a solenoid valve arrangement for directly switching the overall compressed air volume—a pneumatic connection runs between a compressed air feed and a compressed air port leading to the pneumatic installation and has a single isolating valve;

FIG. 2A, 2B show circuit diagrams of pneumatic systems, each with another embodiment of a compressed air supply installation similar to FIG. 1, wherein the vent valve and the isolating valve are furthermore formed as a double armature solenoid valve—this being for different deenergized states (A, B) of the vent valve with the isolating valve closed when deenergized;

FIG. 3A, 3B show circuit diagrams of pneumatic systems with another embodiment of a compressed air supply installation as a modification of the embodiments in FIG. 2A and FIG. 2B—this being for different deenergized states (A, B) of the vent valve with the isolating valve open when deenergized;

FIG. 4 shows a circuit diagram of a pneumatic system with another, particularly preferred embodiment of a compressed air supply installation according to the second developed variant of the invention, in which the vent valve, as an indirectly switched relay valve, is part of a solenoid valve arrangement for indirectly switching a compressed air volume, wherein the solenoid valve arrangement has a control valve subjected to a total pressure of the main pneumatic line in order to control the relay valve—once again, as in FIG. 1, a pneumatic connection runs between a compressed air feed and a compressed air port leading to the pneumatic installation and has a single isolating valve;

FIG. 5 shows a compressed air supply installation in accordance with FIG. 2A or FIG. 2B with a double armature solenoid valve in a preferred design embodiment;

FIG. 6 shows a graphical representation of an illustrative current amplitude of a control signal against time to illustrate switching currents for a vent valve and an isolating valve, which are obtained via a common control line for the primary valve and the secondary valve—in the context of a double armature solenoid valve in FIG. 2A and FIG. 5;

FIG. 7 shows a graphical representation of a greatly simplified time characteristic of a PWM control signal in the form of a voltage signal and of the associated current signal in relation to threshold currents I_(S) for switching a solenoid valve. I_(H) for holding a solenoid valve in the switched state and I_(R) for returning the solenoid valve to an original state of rest—this being intended to illustrate an illustrative clock rate of a control state change for switching over the controllable isolating valve backward and forward between a first and a second control state—in the context of a double armature solenoid valve in FIG. 2A and FIG. 5;

FIG. 8 shows preferred operating states (A-C) of a pneumatic system during the filling of the pneumatic installation according to the second developed variant shown in FIG. 4;

FIG. 9 shows preferred operating states (A-D) of a pneumatic system during measurement within the pneumatic installation according to the second developed variant shown in FIG. 4;

FIG. 10 shows preferred operating states (A, B) of a pneumatic system during the venting of the pneumatic installation according to the developed second variant shown in FIG. 4;

FIG. 11 shows a circuit diagram of a pneumatic system incorporating a particularly preferred modified embodiment of a compressed air supply installation according to a developed variant that is in addition to that in FIG. 1, in which the isolating valve and vent valves are formed separately but the controllable isolating valve and the controllable vent valve are nevertheless set up to be controlled by means of a control signal common to both;

FIG. 12 shows a circuit diagram of a pneumatic system like FIG. 11, in which two isolating valves are arranged in a common coil former and are formed separately into a vent valve, but the controllable isolating valves and the controllable vent valve are nevertheless set up to be controlled by means of a control signal common to both.

FIG. 1 shows a pneumatic system 101 having a compressed air supply installation 11 and a pneumatic installation 90, in the present case in the form of an air spring installation. The air spring installation has a total of four “bellows” 91, which are each assigned to one wheel of a vehicle (not shown specifically) and form an air spring for the vehicle. Moreover, the air spring installation has a reservoir 92 for storing rapidly available compressed air for the bellows 91. Respective bellows solenoid valves 93 are arranged ahead of the bellows 91 in respective bellows branch lines 99.1, each of said valves serving as an air spring valve for opening or closing an air spring formed by a bellows 91. A reservoir solenoid valve 94 as a reservoir valve is arranged ahead of the reservoir 92 in a reservoir branch line 99.2. The bellows solenoid valves 93 and the reservoir solenoid valve 94 are connected by means of the bellows and reservoir branch lines 99.1, 99.2 to a common pneumatic line forming a gallery line 95. The gallery line 95 is connected pneumatically to a compressed air port 2 of the compressed air supply installation 11 by a further pneumatic line 96. In the present case, the bellows solenoid valves 93 serving as level control valves, together with the reservoir solenoid valve 94, are arranged in a valve block 97 having five valves. Other, modified embodiments (not shown here) can give a different arrangement of the bellows solenoid valves 93 and of the reservoir solenoid valve 94—and it is also possible for fewer solenoid valves to be used as part of the valve block 97. In the present case, the pneumatic installation 90 is provided with a pressure sensor 98, which is connected to the gallery line 95 by a sensor branch line 99.3, enabling a pressure in the gallery line 95 of the pneumatic installation 90 to be measured by means of the pressure sensor 98. In very general terms, a gallery should be taken to mean any kind of header pipe from which branch lines or other pneumatic installations start.

In FIG. 1 the bellows solenoid valves 93 and the reservoir solenoid valve 94 are shown in a deenergized state—wherein the bellows solenoid valves 93 and the reservoir solenoid valve 94 are formed as solenoid valves that are closed when deenergized.

The compressed air supply installation 11 is used to operate the pneumatic installation 90. The compressed air supply installation 11 has a compressed air feed 1 and a compressed air port 2 leading to the pneumatic installation 90. In the present case, the compressed air feed 1 is formed with an air feed 0, an air compressor 51 and a compressed air feed port 52 by means of a suitably designed interface. The air compressor 51 is driven by a drive, in the present case in the form of a motor M. In the present case, the pneumatic connection between the air feed 1 and the compressed air port 2 is formed by a single main pneumatic line 60, which is connected, on the one hand, to the compressed air feed port 52 and, on the other hand, to the compressed air port 2. At the port 2, the pneumatic connection is continued by the further pneumatic line 96 leading to the gallery line 95. An air drier 61, a first restrictor 62 and a controllable isolating valve 63 in the form of a 2/2-way valve designed as a solenoid valve are arranged in the main pneumatic line 60. The restrictor 62 and the isolating valve 63 form a pneumatic series arrangement in the main pneumatic line 60.

The compressed air supply installation 11 furthermore has a vent line 70, which is connected pneumatically to the main pneumatic line 60 and to a vent port 3 leading to the environment. Arranged ahead of the vent port 3 is a vent valve 71 arranged upstream in the vent line 70. In the present case, the vent line 70 is connected to the main pneumatic line 60 at the compressed air feed port 52. A second restrictor 72 and a controllable vent valve 73—which in this case is open when deenergized—is arranged in the vent line 70 in the direction of the vent port 3. A filter 74 is arranged after the vent port 3 leading to the environment. In a similar way, a filter (not shown here) can be arranged ahead of the air feed 0.

The compressed air supply installation 11 shown in FIG. 1 provides the vent valve 73 as a single, directly switched valve for directly switching a compressed air volume in the vent line 70. There is no additional control valve provided in the compressed air supply installation 11.

The vent valve 73 is part of a solenoid valve arrangement 80 formed with the isolating valve 63. The solenoid valve arrangement 80 provides a first coil 81 for the controllable isolating valve 63 and a second coil 82, formed separately from the first coil 81, for the controllable vent valve 73. In particular, the first coil 81 and the second coil 82 are each formed with a separate coil former. However, the controllable isolating valve 63 and the controllable vent valve 73 are set up to be controlled by means of a control signal common to both via a control line 83 common to both. In the present case, the second coil 82 does not have a separate control line but instead is connected to the control line 83.

FIG. 2A and FIG. 2B, which are described cumulatively below, each show a pneumatic system 201, 202 having a pneumatic installation 90 described above and in each case modified embodiments of a compressed air supply installation 21 and 22 respectively. The compressed air supply installations 21, 22 are constructed in a manner substantially similar to compressed air supply installation 11, with the same reference signs being used for identical or similar parts or parts of identical or similar function. To this extent, attention is drawn to the description of compressed air supply installation 11; it is primarily the differences with respect to compressed air supply installation 11 which will be explained below.

Compressed air supply installation 21 has a solenoid valve arrangement 80′ with a controllable isolating valve 63′ and a controllable vent valve 73′. The isolating valve 63′ and the vent valve 73′ are again designed as 2/2-way valves, with the isolating valves 63, 63′ being embodied as directional control valves that are closed when deenergized and the vent valves 73, 73′ being embodied as directional control valves that are opened when deenergized. In the present case, in contrast to the solenoid valve arrangement 80 of compressed air supply installation 11, the controllable isolating valve 63′ is formed with a first coil and the controllable vent valve 73′ is formed with a second coil in the solenoid valve arrangement 80′ of compressed air supply installation 21, with the first and the second coil—in the present case represented symbolically as coil 81′—being formed with a single coil former common to both coils. The coil 81′ is once again connected to a controller (not shown specifically) or to a control module (not shown specifically) by means of a control line 83′, similar to the control line 83. The controller or control module can be part of a vehicle controller (ECU) or can be connected to the vehicle controller. As in compressed air supply installation 11—the some controller or control module is available both for an isolating valve 63, 63′ and for a vent valve 73, 73′. In particular, the coil 81′ of compressed air supply installation 21 is controlled via the control line 83′ by means of a control signal common to the isolating valve 63′ and the vent valve 73′.

A compressed air supply installation 22 of substantially similar construction as part of a pneumatic system 202 is shown in FIG. 2B. In contrast to compressed air supply installation 21, compressed air supply installation 22 has a solenoid valve arrangement 80″ with an isolating valve 63″ and a vent valve 73″, with both the vent valve 73″ and the isolating valve 63″ being formed as 2/2-way valves that are closed when deenergized.

In the embodiments of a compressed air supply installation 11, 21, 22 which are shown in FIG. 1 to FIG. 2B, the controllable isolating valve 63, 63′, 63″ is switched to an open state in a through-flow mode. Otherwise—in the present case in the deenergized state shown—the isolating valve 63, 63′, 63″ is in a closed state, with the result that the pneumatic connection in the form of the main pneumatic line 60 and the further pneumatic line 96 is bidirectionally and completely closed. In other words, the main pneumatic line 60 is completely cut off from the further pneumatic line 96 leading to the gallery line 95. That is to say, the isolating valve 63, 63′, 63″ isolates a gallery line 95 and hence, overall, bellows 91 connected thereto, the reservoir 92 or other pressure chambers from the main pneumatic line 60. This complete decoupling, in accordance with the concept of the invention, of the compressed air supply installation 11, 21, 22 from the pneumatic installation 90 when the isolating valve 63, 63′, 63″ is deenergized and closed allows advantageous operation of the pneumatic installation 90 without the compressed air supply installation 11, 21, 22 being influenced thereby. Owing to the decoupling brought about by the isolating valve 63, 63′, 63″—in the present case in the deenergized and closed state—disadvantageous influences on the compressed air supply installation 11, 21, 22 due to the operation of the pneumatic installation 90 are avoided, in particular, and the pneumatic installation 90 can be operated independently of operation of the compressed air supply installation 11, 21, 22.

For this reason, both air admission to the pneumatic installation 90 and air release from the pneumatic installation 90 are prevented when the isolating valve 63, 63′, 63″ is in the closed state—i.e. the pneumatic connection comprising the main pneumatic line 60 and the further pneumatic line 96 is bidirectionally and completely closed for a compressed air flow. In the present case, the pneumatic connection between the air drier 61 and the gallery line 95 is bidirectionally and completely closed in the closed state of the isolating valve 63, 63′, 63″. Among the advantageous effects of this is that the relatively large volume of the air drier 61 can be left out of account for states of the pneumatic installation 90 and, conversely, the air drier 61 is not affected in the event of movements of compressed air in the pneumatic installation 90.

FIG. 3A and FIG. 3B show further modifications of compressed air supply installations 23 and 24, respectively, as part of pneumatic systems 203 and 204, respectively. While otherwise being similar to compressed air supply installations 21, 22, compressed air supply installations 23, 24 are formed with solenoid valve arrangements 80′″ and 80 ^(IV) respectively, with isolating valves 63′″ and 63 ^(IV) being embodied as 2/2-way valves that are open when deenergized. The 2/2-way valves, which are open when deenergized in this way, can be implemented for the solenoid valve arrangements 80′″ and 80 ^(IV) in combination with vent valves 73′″ and 73 ^(IV) as 2/2-way valves that are closed when deenergized or open when deenergized. In the case of vent valves 73, 73′,73 ^(IV) that are open when deenergized, a nonreturn valve 71 is provided in the vent line 70 in order to close the compressed air supply installation 11, 21, 23 with respect to the environment.

FIG. 4 shows another particularly preferred embodiment of a compressed air supply installation 41 as part of a pneumatic system 401 for supplying a pneumatic installation 90. Once again, the same reference signs are used for identical or similar parts or parts of identical or similar function. It is, in particular, the differences with respect to compressed air supply installations 11, 21, 22, 23, 24 which are explained below and, otherwise, attention is drawn to the previous descriptions. Once again, compressed air supply installation 41 has a main pneumatic line 60 and a vent line 70. As in the embodiments explained above, an air drier 61, a first restrictor 62 and a controllable isolating valve 163 are arranged in the main pneumatic line 60. The controllable isolating valve 163 and the restrictor 62 form a series arrangement in the main pneumatic line 60 such that the pneumatic connection comprising the main pneumatic line 60 and the pneumatic line 96 can be bidirectionally and completely closed for a compressed air flow. The vent line 70 is connected to the main pneumatic line 60 at a compressed air feed port 52 and has a controllable vent valve 173 between the compressed air feed port 52 and the vent port 3. In contrast to the embodiments explained above, the isolating valve 163 and the vent valve 173 are part of a solenoid valve arrangement 180 for indirectly switching a compressed air volume. In this case, the vent valve 173, as an indirectly switched relay valve, is part of the solenoid valve arrangement 180, which is controlled by a control valve 175. In the present case, the control valve 175 is subjected to a total pressure of a pressurized flow in the main pneumatic line 60 via a branch line 160 starting from the main pneumatic line 60. Depending on the design of the first restrictor 62, the control valve 175 can also be subjected to a partial pressure of the main pneumatic line 60.

A control valve 175 subjected to only a partial pressure for controlling the relay valve 173, in particular, allows relatively quick venting of the compressed air supply installation 41 since a pilot control pressure is relatively low. In the present case, the control valve 175 of the solenoid valve arrangement 180 is specifically in a state in which it is deenergized when closed. Depending on the design of the restrictor 62, the control current to switch the control valve 175 to the state in which it is open for the branch line 160 so as to bring the relay valve 173 into a pilot-controlled state will be higher or lower. Depending on the design, it then requires only a minimal operating pressure to transfer the relay valve 173 into the open state. The advantage of a quick-venting solenoid valve arrangement 180 is that, by virtue of the relatively small nominal width of the first restrictor 62 in comparison with the larger nominal width of the second restrictor 72, only a small part of the total pressure of a compressed air volume in the main pneumatic line 60 is required to control the relay valve 173 via the control valve 175. Nevertheless, the main pressure volume is vented to the vent port 3 via the vent line 70, the restrictor 72 and the relay valve 173. One advantage of this quick-venting solenoid valve arrangement 180 in the compressed air supply installation 41 is that it is not necessary to switch the entire compressed air volume by means of a single solenoid valve but rather just a small part of a partial compressed air volume via the branch line 160 leading to the control valve 175 is sufficient. This design, more or less a valve arrangement that is in principle positively actuated, allows the operating pressure to be increased to a comparatively high pressure level and, at the same time, the switching of large compressed air volumes by means of the relay valve 173 is made possible. The relay valve 173 can be designed with a relatively large nominal width. Moreover, the ratio of the nominal width of the first restrictor 62 to the nominal width of the second restrictor 72 is formed in such a way that effective regeneration of the air drier 61 is nevertheless possible when the compressed air supply installation 41 is vented.

In the deenergized and closed state, the control valve 175 is open toward the vent port 3 via the further branch line 170, wherein the further branch line 170 is brought together with the vent line 70 ahead of the vent port 3.

FIG. 5 shows, in a view (A), a particularly preferred design embodiment of a compressed air supply installation 30 as part of a pneumatic system 300 (not shown specifically). Here, view (A) shows the compressed air supply installation 30 in a generalized way with a number of regions. A drive in the form of the motor M for driving the air compressor 51 (shown schematically in the second region 32) is arranged in the first region 31 (not shown specifically). Here, the air compressor 51 has a piston (not designated specifically), which can be moved backward and forward in a compression chamber and is driven by the motor M via a shaft and a connecting rod. In the compression chamber, air is fed in via an air feed interface E0 of the abovementioned air feed 0. Compressed air at the outlet of the compression chamber is transferred via a valve or a similar interface component to a compressed air feed interface E1 for the abovementioned compressed air feed 1. The compressed air feed interface E1 is assigned to the compressed air feed port of the embodiments explained above. The compressed air is then discharged into a third region 33 of the compressed air supply installation, which third region 33 embodies the main pneumatic line 60 and vent line 70 with the internal components mentioned, in particular the solenoid valve arrangement MVA illustrated schematically in view (A). In principle, the solenoid valve arrangement MVA can be formed by any of the solenoid valve arrangements 80, 80′, 80″, 80′″, 80 ^(IV), 180 explained above or below. In particular, the third region 33 contains the air drier 61 with a drying canister 34, which is filled with desiccating granules and through which a compressed air flow from the main pneumatic line 60 can flow—whether as a venting flow P or as a supply flow P. The regions are assigned corresponding housing parts A, B, C, which are sealed off from one another by one or more seals D, if appropriate. The third region 33 is, in particular, assigned a housing part C and a cover T, which closes off housing part C at the end. The cover T forms a compressed air supply interface E2 for the abovementioned compressed air port 2 leading to the pneumatic installation 90. As explained, the compressed air port 2 leads to the further pneumatic line 96 and to the gallery line 95. In the present case, the first restrictor 62, which is assigned to an isolating valve of the solenoid valve arrangement MVA, is formed within a defined nominal width as an aperture in the drying canister 34 and cover T. The cover T also forms a vent interface E3 for the abovementioned vent port 3. Finally, the cover T also forms an electrical control interface S for attachment of the abovementioned control line 83, 83′, 83″, 83′″, 83 ^(IV) to the solenoid valve arrangement MVA. The dimensions of the cover T are largely congruent with an end contour of the drying canister 34, and the cover can be mounted with an almost perfect fit on the drying canister 34.

Housing part C is formed by a wall W of the drying canister 34, which is filled with desiccating granules, and by the cover T. The desiccating granules are held together under pressure in the drying canister 34 by a spring F. At the end of the drying canister 34, the wall W in turn forms a recess G, which is arranged symmetrically and, in the present case, centrally and parallel to an axis of the drying canister 34. A vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 and an isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 in the form of the solenoid valve arrangement MVA are accommodated in the recess G, symmetrically with the axis of the drying canister 34. At the end, the cover T closes off the recess G in the leaktight manner mentioned, together with the solenoid valve arrangement MVA situated therein.

By means of the illustrated U-shaped arrangement of the regions 31, 32, 33 and of the associated housing parts A, B, C, space-saving compressed air supply installation 30 is made available, which furthermore allows horizontal interfaces, namely as S, E0, E1, E2, E3. Moreover, a weight saving is achieved by virtue of the fact that the outer contour of the drying canister 34 of the air drier 61 and the cover T are used as part of the housing arrangement of the compressed air supply installation 30. In the present case, the solenoid valve arrangement MVA is surrounded on three sides in the recess G of the drying canister 34. From this, it can be seen that the recess G is free of desiccant. A venting flow P from the gallery line 95, said flow being indicated by solid arrows, can be passed via the compressed air supply interface E2 and the vent interface E3 in the cover T, if required. As shown by the symbolically indicated venting flow P, the air can flow through the air drier 61 in the opposite direction to a supply flow P indicated by dashes in order to perform regeneration. The supply flow P indicated by dashed arrows is used to supply the pneumatic installation 90 via the pneumatic line 96 and the gallery line 95 and flows from the compressed air feed interface E1 to the compressed air supply interface E2 of the compressed air port 2.

View (B) in FIG. 5 shows a solenoid valve arrangement MVA which is in the form of a double armature solenoid valve—in the present case to form a solenoid valve arrangement 80′ according to FIG. 2A. In the double armature solenoid valve, a primary valve I is implemented in order to form an isolating valve 63′—in other embodiments it is also used to form an isolating valve 63, 63″, 63′″, 63′″, 163 explained above. A secondary valve II is likewise implemented in the solenoid valve arrangement MVA in the form of a double armature solenoid valve in order to form a vent valve 73′—in other embodiments it is also used to form a vent valve 73, 73″, 73′″, 73 ^(IV), 173 explained above. The primary valve I has a primary armature Ib, which carries a first sealing element Ia and which is held on a valve seat Id of the primary valve I by a valve spring Ic. In the present case, the primary valve I is closed when deenergized and opens when the coil former III common to the primary valve I and the secondary valve II is energized, said coil former serving to form the coil—in the present case coil 81′—common to the primary valve I and the secondary valve II. In a very similar way, the secondary valve II has a secondary armature Iib, which carries a second sealing element Iia of the secondary valve II and is likewise arranged as a core of a coil common to the primary valve I and the secondary valve in the coil former III of the double armature solenoid valve. In the present case, the second sealing element IIa is raised from the valve seat IId by the valve spring IIc of the secondary valve and thus secondary valve II is a directional control valve that is open when deenergized. In particular, it is a 2/2-way valve, like the vent valve 73′ of compressed air supply installation 21. As a result, in the present case, a pneumatic connection in the compressed air supply line 70 is open to the vent interface E3 of the vent port 3. Once again, the venting flow P is indicated symbolically as a solid arrow.

Using the double armature solenoid valve MVA, it is possible in a particularly advantageous manner in the present case to control both a controllable isolating valve—here implemented as primary valve I—and the controllable vent valve—here implemented as secondary valve II—by means of a control signal common to both in order, on the one hand, to open the primary valve I and, on the other hand, to close the secondary valve II upon energization. This is explained by way of example with reference to FIG. 2A:

If compressed air from a compressed air flow is required—e.g. for raising a vehicle by filling the bellows 91 or for filling the reservoir 92—the primary valve I and the secondary valve II are switched on, i.e. the coil former III is supplied with a control signal in the form of a high control current sufficient to switch the primary and secondary valves I, II. As a result, the primary valve I switches through, i.e. opens. The secondary valve II goes from the open position to a blocking position. This functional position of the double armature solenoid valve thus allows filling of the pneumatic installation 90 from the compressed air feed 1. If, on the other hand, the pneumatic installation 90 is to be vented, e.g. to lower the vehicle, then, in the present case, only the primary valve I is switched on, i.e. the primary valve I opens, while the secondary valve remains in the open position thereof, which is shown in the view in FIG. 3B. A sufficiently low level for a corresponding control current is chosen to ensure that only the primary valve I switches. The nominal widths of the first restrictor 62 and the second restrictor 72 which are suitable for the air admission and venting functions—in the present case a nominal width of in each case 2.5 mm—are formed through the formation of the nominal widths of the valve seats Id and IId of the primary valve I and of the secondary valve II, respectively.

FIG. 6 shows, by way of example, a symbolic representation of a current amplitude SA of a control current for switching a double armature solenoid valve MVA in the functional position, shown in FIG. 2A, of a controllable isolating valve 63 ^(I) in combination with a vent valve 73 ^(I) which is open when deenergized for air admission to and venting of the pneumatic installation 90. In this case, the isolating valve 63 ^(I) assumes the role of the primary valve I of a solenoid valve arrangement MVA, and the vent valve 73 ^(I) assumes the role of the secondary valve II of the solenoid valve arrangement MVA. In the present case, the current amplitude SA is shown against a hypothetical time profile t and can be used, for example, for learning a precise switching point of the primary valve I and/or the secondary valve II. This can take place in the context of a diagnostic job for a vehicle controller ECU, for example. The graphic in FIG. 6 shows a regulated current amplitude SA, leading, when a first current amplitude SA₁ is exceeded, to the primary valve I passing, i.e. being switched over, from the deenergized and closed state to an open switching state—owing to the setting of a valve spring Ic of the primary valve I. When a second current amplitude SA₂ is exceeded, said current being higher in the present case, the secondary valve II switches in addition, i.e. makes a transition from the deenergized and open state to a switching state which corresponds to the closed state of the secondary valve II. If the control current amplitude is reduced, the secondary valve then opens when a third current amplitude SA₃ is undershot—taking into account a certain hysteresis—i.e. the secondary valve II then makes a transition from the energized and closed state to a switching state in which it is once again open, said state occurring at a lower energization level. When a fourth, in the present case lower, current amplitude SA₄ is undershot, the primary valve I makes a transition from the energized and open switching state back to the deenergized and closed switching state.

Learning of the current amplitudes SA₁, SA₂, SA₃, SA₄ thus described as relevant switching points for an on/off switching state transition of the primary valve I and the secondary valve II can take place when the vehicle is started or, alternatively, only after replacement of a component or components. In fact, an exact identification of a point in time of a movement of a valve armature, namely of a primary armature Ib or of a secondary armature Iib, is not readily discernible. However, learning the switching points makes possible precise switching of the primary valve I and of the secondary valve II in the double armature solenoid valve arrangement MVA. A learning procedure can advantageously be stored as a diagnostic job in the vehicle controller in a module of the vehicle controller, i.e. in the ECU. Apart from the reversed pneumatic control state of the deenergized and closed vent valve 73 ^(II), the abovementioned profile also applies to the double armature solenoid valve MVA in FIG. 2B. A possible sequence based on FIG. 2A could be as follows:

1. In the case of the second current amplitude SA₂: switch through primary valve I and secondary valve II and fill bellows 91.

2. In the case of the fourth current amplitude SA₄: switch off primary valve I and secondary valve II and put them in the deenergized state.

3. In the case of the first current amplitude SA₁: switch on primary valve I, i.e. isolating valve 63′, and measure the pressure in the main pneumatic line 60 and/or in the pneumatic line 96 or the gallery line 95.

4. Slowly increase the current amplitude SA for primary valve I and secondary valve II. The result observed is that, as the pressure drop begins, the first current amplitude SA₁ is reached by the primary valve I, i.e. the isolating valve 63′ is opened and opens the main pneumatic line 60 to the pneumatic line 96 and the gallery line 95, this being observable from the start of the pressure drop.

5. Increase current amplitude SA further. If the pressure does not drop further, the result is that the second current amplitude SA₂ of the secondary valve II is reached. The result of the transition of the secondary valve II from the open switching state to the closed switching state is that the pressure ceases to fall.

By means of 4. and 5., the first and second current amplitudes SA₁, SA₂ of the switch-on currents are determined.

6. In the further steps, the current amplitude SA is reduced again. If an initially constant pressure and then a decline in pressure is observed, the third current amplitude SA₃ for switching off the secondary valve II has been reached. Since the secondary valve II, which is formed as a vent valve 73 ^(I), opens, this is observable from the decline in pressure.

7. The current amplitude SA is reduced further until there is no further decline. The fourth current amplitude SA₄ which is now present corresponds to the switching current for switching off the primary valve I, i.e. the switching current is below the current amplitude SA₄ at which the primary valve I, namely the isolating valve 63′, closes, i.e. compressed air remains in the compressed air supply installation.

The current amplitudes SA₁, SA₂, SA₃, SA₄ precisely determined in this way for switching points can be used for the further, optimized functional operation of the primary valve I and of the secondary valve II, i.e. in the present case of an isolating valve 63′ and of a vent valve 73′. Switching points for isolating valves 63, 63″, 63′″, 163 ^(IV), 163 and vent valves 73, 73″, 73′″, 73 ^(IV), 173 can be determined in a similar way.

Thus, for example, the function of the compressed air supply installation 41 in FIG. 4 in respect of the isolating valve 163 and of the vent valve 173 is similar to the functioning of the compressed air supply installations 11, 21, 22, 23, 24 explained above. In particular, the current amplitudes for the switching currents in respect of a primary valve I—here the isolating valve 163—and a secondary valve II—here the control and relay valve arrangement comprising control valve 175 and relay valve 173—can be chosen according to a procedure similar to that described in FIG. 6. An arrangement of solenoid valve arrangement 180 instead of solenoid valve arrangement MVA in view (A) of FIG. 5 is likewise possible, and therefore a relatively compact embodiment of solenoid valve arrangement 180 in a compressed air supply installation 41 is also possible.

A sequence of current amplitudes for changing the switching states of the isolating valve 63′″, 63 ^(IV) and of the vent valve 73′″ or 73 ^(IV) can likewise be chosen in a manner similar to the current amplitudes shown in FIG. 6, but the switching states of the valves 63′″, 73′″ and 63 ^(IV), 73 ^(IV) are correspondingly different. In the case of a current amplitude SA₁, for example, the isolating valve 63′″ or 63 ^(IV) acting as the primary valve I is closed, with the result that, in the case of energization with a current amplitude SA₁, compressed air supply installation 23 assumes a switching state which corresponds to the deenergized switching state of compressed air supply installation 21. When solenoid valve arrangement 80′″ is energized with a current amplitude SA₁, solenoid valve arrangement 80′″ will likewise assume a switching state which corresponds to the deenergized switching state of solenoid valve arrangement 80″.

Both solenoid valve arrangement 80′″ and solenoid valve arrangement 80 ^(IV) can be implemented in a compressed air supply installation 30 instead of the symbolically represented solenoid valve arrangement MVA.

By means of the graphical representation of a simplified time characteristic of a PWM control signal 190, FIG. 7 illustrates a particularly preferred possibility for switching over the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 of FIG. 1 to FIG. 4 between a first and a second control state of an isolating valve in a through-flow mode. In the present case, a symbolic equivalent circuit diagram ES is shown in the detail X_(ES) for the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 of FIG. 1 to FIG. 4 in the main pneumatic line 60. In the detail X_(ES), a control state change U resulting from the switchover process is indicated by a dashed double arrow. In this case, the first control state (i) is assigned to a state in which the valve is virtually closed when deenergized. In this case, the second control state (ii) is assigned to a state in which the valve is open when energized. A similar control signal can also be used, in a modified embodiment (not described further here), to switch over a vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 between a first and a second control state in a through-flow mode. In the case of the vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 too, a first control state would in the present case be assigned to a closed state and a second control state would be assigned to an open state. In particular, the PWM control signal illustrated in the present case in FIG. 7 is suitable for switching over the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 backward and forward between a first (i) and a second (ii) control state at a clock rate of a control state change U. It is thereby possible to set an effective nominal width N_(eff) of the isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 in series arrangement with the restrictor 62 and/or of the vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173.

To be more specific, in this regard a voltage signal 191 in the form of PWM voltage pulses of the PWM control signal 190 is shown in FIG. 7. A current signal 192 resulting from the voltage signal 191 is likewise shown. The current signal 192 of the PWM control signal corresponds in simplified form to a current profile in a coil former of a controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or of a controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 when a voltage signal 191 is applied to the coil former in accordance with the PWM control signal 190.

The PWM control signal 190 has a signal region 190.1 assigned to a first control state (i) and a signal region 190.2 assigned to a second control state (ii). The signal regions 190.1, 190.2 alternate at a predetermined clock rate and, in this way, bring about a control state change U between a first control state and a second control state (i), (ii). In principle, the clock rate can be set between 4 Hz and 20 Hz—FIG. 7 shows a clock rate of 10 Hz. In particular, the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 are thus switched backward and forward at the clock rate of 10 Hz as part of the control state change U, between a first control state (i) (in signal region 190.1) assigned to the closed state and a second control state (ii) (in signal region 190.2) assigned to the open state. During the control state change U, i.e. for signal regions 190.1, 190.2, the controllable isolating valve and/or vent valve is/are in the through-flow mode. In other words, a controllable valve—in the present case the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173—is guided toward the closed state in the first signal region 190.1, without the closed state being reached; this tendency corresponds to the first control state (i). In a corresponding manner, a controllable valve—in the present case the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173—is guided toward the open state in the second signal region 190.2, without the open state being reached; this tendency corresponds to the second control state (ii). In a modified embodiment, it is, of course, also possible for the closed state of the controllable valve to be reached during a signal region 190.1 without departing from the concept of the present embodiment. In a modified embodiment, it is, of course, also possible for the open state of the controllable valve to be reached during a signal region 190.2 without departing from the concept of the present embodiment. As a preferred option in the present case, however, the clock rate of the control state change U, i.e. the clock rate of an alternation between the signal regions 190.1 and 190.2, is about 10 Hz. In principle, a clock rate of this kind of between 4 and 20 Hz can be chosen. Basically, this has the effect that—in the case of a higher clock rate—a controllable valve moves backward and forward between a completely closed state and a completely open state without the completely open or completely closed state necessarily being reached ultimately, although it could be reached at a lower clock rate.

To be more specific, as part of the control state change U the clocked switchover of a controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or of a controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 in the through-flow mode takes place as follows: in the first signal region 190.1, the pulse widths t₃ in relation to the interpulse widths t₄ of a voltage signal 191 in the form of PWM voltage pulses are chosen in such a way that a current signal 192 to which they give rise is less than or equal to a reset current I_(R). In other words, a pulse/no pulse ratio t₃/t₄ is chosen to be so small that a current signal 192 during the pulse time t₃ can rise only to a value less than or equal to the reset current I_(R) and, during the interpulse time t₄, drops back again by a sufficient amount. In signal region 190.1, a controllable valve is thus not switched and remains in a control state (i) assigned to the “deenergized” and closed state. For example, this state corresponds to the deenergized and closed state of the isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 shown in FIG. 1, FIG. 2A, FIG. 2B and FIG. 4.

In a second signal region 190.2, a pulse/no pulse ratio t₁/t₂ of the voltage signal 191 in the form of the PWM voltage pulses is chosen to be greater than in the first signal region 190.1. In other words, the pulse times t₁ are then chosen in such a way that a current signal 192 has sufficient time to rise to a switching current I_(S) and, during the interpulse times t₂, at least does not fall below the reset current I_(R). This has the effect that, when the switching current I_(S) of the current signal 192 is reached or exceeded, a controllable valve is switched through—this being an isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 in the case of FIG. 1, FIG. 2A, FIG. 2B and FIG. 4—that is to say is transferred from a deenergized and closed state to an energized open state.

As can be seen from the characteristic of the PWM control signal 190 shown in FIG. 7, the time duration of a second signal region 190.2 is limited to such an extent that a completely open state is not fully reached in the associated control state (ii) of the controllable valve. On the contrary, a current signal 192 falls below the reset current I_(R) at a time t_(R). Before the completely open state of the controllable valve—namely the isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163—is reached, a transition back to a first signal region 190.1, in which the controllable valve can make a transition to a control state (i) assigned to the deenergized and dosed state, takes place in accordance with the clock rate, illustrated in FIG. 7, of a control state change of 10 Hz of the PWM control signal 190.

The duration of the first signal region 190.1 is once again limited in time in accordance with the clock rate shown in such a way that a second signal region 190.2 follows before the completely closed state of the controllable valve is finally reached. This has the effect that, when the switching current I_(S) is reached at time t_(S), the controllable valve is transferred back to an open state.

The dynamic backward and forward guidance of the controllable valve—i.e. of the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or of the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173—in this way, at a predetermined clock rate of 10 Hz, between a first control state (i) assigned to the closed state and the second control state (ii) assigned to the open state has the effect that, in the through-flow mode of the controllable valve, it is possible to exercise closed-loop and/or open-loop control over the flow rate of the controllable valve by means of an effective nominal width N_(eff) of the controllable valve, which can be adjusted in this way. By switching backward and forward between a closed state, the actual nominal width of the controllable valve in the completely closed state is in practice reduced to the effective nominal width N_(eff) which is assumed during the control state change U, i.e. in the state of dynamic backward and forward switching. In particular, the continuous control state change U of the controllable valve between a first and a second control state (i), (ii) at a clock rate of a control state change U between a first signal region 190.1 and a second signal region 190.2 has the effect that an effective nominal width N_(eff) of a series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 is below an actual nominal width of the restricting means 62 in the completely open state of the isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163. In this way, an effective nominal width N_(eff) that can be subjected to closed-loop and/or open-loop control is achieved in practice. However, this does not exclude the possibility in the limiting case of completely closing or completely opening the series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163. In the context of a specific embodiment, the nominal width of a main pneumatic line 60 can be in a range above 4 mm, for example. The actual nominal width of a restricting means 62 can be between 1 and 3 mm, in the present case 2.5 mm, for example. By means of a control state change U, as described above, of a controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 at a predetermined clock rate, the effective nominal width N_(eff) of the series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 can in this way be adjusted to below the actual nominal width of the restricting means of 2.5 mm. For example, the effective nominal width N_(eff) of the series arrangement can be adjusted in a range between 0.6 mm and 2.5 mm—depending on the clock rate chosen—by a clocked control state change U of the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163.

In order, on the other hand, to transfer the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 to a completely closed state in the regularly occurring limiting case, a voltage signal 191 can be provided for a longer period of time than the first signal region 190.1, with the result that, in that case, a current signal 192 remains below the reset current I_(R) for a longer time. It is else possible to completely deenergize the isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163. In this case, the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 makes a transition completely into the closed state and can close the main pneumatic line 60 bidirectionally and completely. Conversely, in a third signal region 190.3 illustrated by way of example, a voltage signal 191 with a pulse/no pulse ratio t₅/t₆ can be chosen in such a way that a current signal 192 can rise in accordance with the pulse rate of the PWM control signal to a holding current I_(H). A holding current I_(H) is sufficient to hold a controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or a controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 in an energized and open state. A pulse rate of the PWM control signal itself can be chosen in a range of about 10 kHz—irrespective of the pulse/no pulse ratio t₁:t₂ or t₃:t₄ or t₅:t₆.

FIG. 7 shows the resulting characteristic of a PWM signal 190, in which, first of all, a through-flow mode of the controllable valve is influenced by partial opening and c losing of the controllable valve by clocked control state change U—i.e. alternation of the first and second signal regions 190.1 and 190.2. In this way, a flow rate can be subjected to closed-loop and/or open-loop control by means of the clock rate of the control state change U and the above-described effective nominal width N_(eff) of the valve brought about thereby. In the region of the clocked control state change U between the first and second control states (i), (ii)—which in the present case spans the alternating first and second signal regions 190.1 and 190.2—the series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 is in the through-flow mode, in which an effective nominal width N_(eff) of the series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 is below an actual nominal width of the restricting means 62. In a further region, which is assigned to the third signal region 190.3, the series arrangement is completely open and the nominal width thereof corresponds to the static nominal width of the restricting means 62, in the present case 2.5 mm. In a region (not shown) in which a current signal 192 is below a reset current I_(R) (similar to the first signal region 190.1), the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 makes a transition into a completely closed state—as illustrated in FIG. 1, FIG. 2A, FIG. 2B and FIG. 4—and closes the pneumatic connection comprising the main pneumatic line 60 and the pneumatic line 96 bidirectionally and completely.

In summary, therefore, in the present case a first control state (i) is assigned to a first PWM control signal in the first signal region 190.1, and a second control state (ii) is assigned to a second PWM control signal in the second signal region 190.2. The clock rate of the control state change U can be modified in accordance with different control parameters. It is also possible to modify a duration of the first and second signal regions 190.1 and 190.2 in accordance with a very wide range of control parameters. For this purpose, the spacing between times t_(S) and t_(R) can be modified according to requirements in accordance with a control parameter. For example, a total opening time of a controllable valve can be set according to requirements in the through-flow mode. For this purpose, the duration of a first signal region 190.1 can be lengthened or shortened, for example, i.e. the spacing between times t_(R) and t_(S) can be lengthened or shortened. A switching speed can be influenced by changing the clock rate, i.e. the alternation between the first and second signal regions 190.1, 190.2. In principle, a large number of control parameters can be used to adjust the effective nominal width of the series arrangement, it being possible for said control parameters to be supplied by a vehicle controller or a state of a pneumatic installation 90 or the state of a compressed air supply installation 11, 21, 30, 41, for example. Thus, for example, the switching speed of a controllable valve and/or a total opening time in the through-flow mode or a total closing time in the isolating mode can be adjusted. It is also possible for a first control state and/or second control state to be adjusted in a variable manner. In other words, a control state change of the kind described with reference to FIG. 7 does not necessarily have to take place between first and second signal regions 190.1, 190.2 that are always the same. As already indicated above, an actual switching state of a controllable valve can be adjusted by changing the first and second control states—i.e. by means of the first and second signal regions 190.1, 190.2—in particular can be continuously adjusted. The actual control state of a controllable valve can define virtually any position of an armature of the valve continuously between a completely closed and a completely open position.

These and other possibilities for adjusting a control state change U can be performed in accordance with a discharge characteristic of a pneumatic installation 90 and/or of a compressed air supply installation 11, 21, 22, 23, 24, 30, 41, for example. A gallery pressure in a pneumatic installation can also serve as a control parameter. A gallery pressure can be measured by a pressure sensor 98 of the kind connected to a gallery line 95 via the sensor branch line 99.3 in FIG. 1, for example. It is also possible for a current air release situation to be the decisive factor for appropriate adjustment of the effective nominal width N_(eff) of the series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163. Moreover, an actual distance between a setpoint and an actual value of an air release or air admission situation can be used as a control parameter for a control state change. If, for example, the distance between the setpoint and the actual value of a gallery pressure of the pneumatic installation is relatively large, this can be used to initiate a relatively quick venting process. For this purpose, the clock rate of a control state change can be reduced or the duration of a second signal region 190.2 can be lengthened, for example. It is likewise possible for an air drier regeneration requirement to be a decisive factor in the adjustment of the effective nominal width N_(eff). On the other hand, acoustic values of a compressed air supply installation 11, 21, 22, 23, 24, 30, 41 and/or of a pneumatic installation 90 can be used to make a venting process relatively quiet and, in particular, to prevent an explosive release of air. For this purpose, it can be specified, in the context of a particularly preferred embodiment, that a completely open state of the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 is to be avoided for certain pressure values of the gallery pressure and that a clock rate of a control state change U—i.e. an alternation between the signal regions 190.1 and 190.2—is to take place at a minimum clock rate. Above a certain pressure level of the gallery pressure, a minimum clock rate can ensure that a pressure pulse is divided into sufficiently short pressure pulses of sufficiently low amplitude, which cannot lead to an explosive release of air.

In the context of a particularly preferred embodiment of a control method for a compressed air supply installation, provision is made for a flow rate of the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and/or the controllable vent valve 73, 73′, 73″, 73′″, 73 ^(IV), 173 in the through-flow mode to be subjected to closed-loop and/or open-loop control, wherein at least one of the valves is switched backward and forward between a first and a second control state at a clock rate of a control state change. Depending on a pressure value of the pneumatic installation 90, in particular a gallery pressure, the control method can envisage that, in the through-flow mode, a minimum clock rate that is dependent on the pressure value for the clock rate is provided in order to avoid an explosive release of air.

The result is that the solenoid valve arrangement 80, 80′, 80″, 80′″, 80 ^(IV), 180 of a compressed air supply installation 11, 21, 22, 23, 24, 30, 41 which can be switched backward and forward with a clocked control state change in the through-flow mode offers the possibility of enabling an effective nominal width N_(eff) of a series arrangement comprising the restricting means 62 and the controllable isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 to be subjected to closed-loop and/or open-loop control. It is thereby possible, in the through-flow mode, not only to exercise closed-loop and/or open-loop control over a flow rate but, in addition, to avoid disadvantageous situations such as an explosive release of air. It is also possible to adjust venting, air admission or other operating states of the compressed air supply installation 11, 21, 22, 23, 24, 30, 41 in accordance with the abovementioned control parameters.

A combination of a vent valve 73, 73′ which is open when deenergized and an isolating valve 63′ which is closed when deenergized has proven particularly advantageous—as illustrated in FIG. 1 and FIG. 2A. In this case, an isolating valve 63, 63′ can initially be switched on its own for a venting process and transferred to the through-flow mode for this purpose. For a combination of a vent valve 73″ which is closed when deenergized and an isolating valve 63″ which is closed when deenergized, it has proven advantageous for a venting process initially to switch the vent valve before the open state and only then or simultaneously to transfer the isolating valve to a through-flow mode. A through-flow mode can be explained by way of example with reference to FIG. 7.

Following on from FIG. 4, FIG. 8 to FIG. 10, which apply to the compressed air supply installation 41 and the pneumatic installation 90 in the form of an air spring installation shown in FIG. 4, show how selected functional positions of the compressed air supply installation 41 and of the pneumatic installation 90 can be used for different operating positions of the pneumatic system 401. Attention is drawn here to the fundamental description of FIG. 4.

FIG. 8 first of all shows, in views (A), (B), (C), different operating positions which serve for filling the pneumatic installation 90. In all the operating positions, the controllable isolating valve 163, i.e. the primary valve of the solenoid valve arrangement 180, is in an energized and open position. That is to say that the main pneumatic line 60 and hence the compressed air supply installation 41 is open to the further pneumatic line 96 and to the gallery line 95. In particular, it is advantageous if the controllable isolating valve 163 is in a completely open state during filling since, in most situations, there is no reason to reduce the effective nominal width of the series arrangement comprising the restricting means 62 and the controllable isolating valve to below the actual nominal width of the restricting means 62.

View (A) of FIG. 8 shows a functional position of the pneumatic system 401 in which the reservoir 92 of the pneumatic installation 90 is being filled. For this purpose, the reservoir solenoid valve 94 arranged ahead of the reservoir 92 is energized and hence open. Via the main pneumatic line 60, the further pneumatic line 96 and the gallery line 95, the reservoir 92 can be filled with the compressed air of the compressed air supply installation 41 delivered from the compressed air feed 1. In the present case, the reservoir 92 is filled up to a reservoir pressure in a range of between 13.5 and 18 bar.

View (B) of FIG. 8 shows an operating position of the pneumatic system 401 in which the bellows 91 are being filled with compressed air. The functional position of the compressed air supply installation 41 corresponds to view (A) of FIG. 8, and therefore attention is drawn here to the description of the functional position of the compressed air supply installation 41 in view (A) of FIG. 8. In contrast to the operating position of the pneumatic system 401 and to filling of the reservoir 92, the upstream reservoir solenoid valve 94 ahead of the reservoir 92 is in a deenergized and closed position in the present case. On the other hand, the upstream bellows solenoid valves 93 ahead of the bellows 91 are energized and open, enabling the compressed air made available from the pressure feed 1 to be delivered via the main pneumatic line 60 and the further pneumatic line 96 into the gallery line 95 and into the bellows 91. In the present case, the bellows 91 are filled up to a bellows pressure in a range of from 5 to 12 bar. View (C) of FIG. 8 shows an operating position of the pneumatic system 401 in which the bellows 91 of the pneumatic installation 90 are filled with compressed air both from the reservoir 92 and from the compressed air feed 1. For this purpose, both the bellows solenoid valves 93 arranged ahead of the bellows 91 and the reservoir solenoid valve 94 arranged ahead of the reservoir 92 are energized and therefore open. In the operating position of the pneumatic system 401 which is shown in view (C) of FIG. 8, the delivery pressure of the compressed air feed 1 corresponds at least to the reservoir pressure of the reservoir 92, with the result that the bellows 91 can be filled equally from the reservoir 92 and from the gallery line 95.

FIG. 9 shows, in views (A) to (D), further operating positions of a pneumatic system 401, which are suitable for cross-connecting bellows 91 and for measuring operations in the pneumatic installation 90. In all cases of the operating positions of the pneumatic system 401 in views (A) to (D) of FIG. 9, the compressed air supply installation 41 is in the functional position shown in view (A). In this case, the controllable isolating valve 163 serving as the primary valve of the solenoid valve arrangement 180 is in a completely closed state, i.e. is closed when deenergized. As a result, the main pneumatic line 60 is bidirectionally and completely closed for a compressed air flow to the further pneumatic line 96 and to the gallery line 95. The Compressed air supply installation 41 is thus decoupled from the pneumatic installation 90. This has the advantageous result that the operating positions of the pneumatic system 401 which are shown in views (A) to (D) can be implemented in the pneumatic installation 90 without affecting or indeed negatively affecting the compressed air supply installation 41, in particular the air drier thereof.

The operating position of the pneumatic system 401 which is shown in view (A) is used to fill the bellows 91 of the pneumatic installation 90 from the reservoir 92 thereof. For this purpose, all the bellows solenoid valves 93 and the reservoir solenoid valve 94 arranged ahead of the reservoir and the bellows 91 are energized, i.e. are in an open state. Compressed air stored in the reservoir 92 at a reservoir pressure of about 13.5 to 18 bar can thus flow from the higher compressed air level into the bellows 91 via the gallery line 95, enabling a bellows pressure in a range of from 5 to 12 bar to be achieved.

The operating position of the pneumatic system 401 which is shown in view (B) of FIG. 9 is obtained with the same functional position of the compressed air supply installation 41 as that shown in view (A) of FIG. 9. The operating position shown in view (B) is used to measure a bellows pressure—in this case in a topmost bellows 91 by means of a pressure sensor 98 connected to the gallery line 95 by a sensor branch line 99.3. Accordingly, a reservoir solenoid valve 94 arranged ahead of the reservoir 92 is in a deenergized and closed state, while a bellows solenoid valve 93—in this case the topmost valve—arranged ahead of the bellows 91 to be measured is energized and thus in an open state. When all the bellows solenoid valves 93 are open, it is also possible, in contrast to the above-mentioned individual measurement, for the bellows pressure of all the bellows 91 to be measured simultaneously. The bellows pressure of all the bellows 91 can thus be equalized via the open bellows solenoid valves 93, and the pressure averaged in this way can be measured by means of the pressure sensor 98.

As with all the further operating positions described, the operating position of the pneumatic system 401 which is shown in view (C) once again uses a functional position of the compressed air supply installation 401 as in view (A) of FIG. 9. The operating position of the pneumatic system 401 of view (C) of FIG. 9 is used to measure the reservoir pressure by means of the pressure sensor 98 in the sensor branch line 99.3 and the gallery line 95. Accordingly, the bellows solenoid valves 93 arranged ahead of the bellows 91 are in a deenergized and closed state, while the reservoir solenoid valve 94 arranged ahead of the reservoir 92 is in an open and energized state.

The operating position of a pneumatic system 401 which is shown in view (D) provides a slight modification of the pneumatic installation 90. In the present case, a pressure sensor 98 is not connected to the gallery line 95 by a sensor branch line 99.3, in contrast to views A to C and E. On the contrary, in view (D) of FIG. 9 a pressure sensor 98 is connected directly to the reservoir 92. It is thus possible to measure a reservoir pressure in the reservoir 92 directly, both when the reservoir solenoid valve 94 is open and when the reservoir solenoid valve 94 is closed.

FIG. 10 shows two further operating positions of a pneumatic system 401 in views (A) and (B), which are used for a venting process. In this case, both the controllable isolating valve 163 of the compressed air supply installation 41 and the vent valve 173 are in the through-flow mode. In the present case, the compressed air supply installation 41 is in a functional position in which the control valve 175 of the solenoid valve arrangement 180, said valve serving as a secondary valve, and the vent valve 173 of the solenoid valve arrangement 180, said valve being formed as a relay valve, are in an open state. In particular, the relay valve is in a completely open state for this purpose, with the result that it is available with a maximum nominal width for a relatively quick venting process. On the other hand, the controllable isolating valve 163 of the solenoid valve arrangement 180, said valve serving as a primary valve, is in a through-flow mode, in which a flow rate of a compressed air flow can be subjected to closed-loop and/or open-loop control. In the present case, this is achieved by a docked control state change of the controllable isolating valve 163 as described with reference to FIG. 7. That is to say that the open position of the controllable isolating valve 163, which is shown in view (A) of FIG. 10, is chosen so that, on the one hand, relatively quick venting can take place and, on the other hand, that acoustic phenomena associated with the compressed air supply installation 41 are kept to a relatively low level. In particular, a clock rate of a control state change is net between a first and a second control state, as described with reference to FIG. 7. A minimum clock rate is chosen in such a way that a pressure pulse from the gallery line 95 and/or from the further pneumatic line 96 is reduced to such an extent that an explosive release of air is reliably avoided.

The latter applies particularly to the operating position of the pneumatic system 401 which is shown in view (A) of FIG. 10, said system being used to vent the pneumatic installation 90 and the compressed air supply installation 41 from the reservoir 92. Since the reservoir pressure is relatively high, being in a range of between 13.5 and 18 bar, this operating position of the pneumatic system 401 tends to trigger an explosive release of air. In the present case, this is avoided, in particular, by the fact that a clocked control state change with a sufficiently high clock rate in accordance with FIG. 7 for the controllable isolating valve 163 is chosen at least for a first phase of the venting process, with the vent valve 173 and the reservoir solenoid valve 94 arranged ahead of the reservoir 92 being in a completely open state. The bellows solenoid valves 93 arranged ahead of the bellows 91 are in a deenergized and closed state.

In a second phase of the venting process—e.g. when the pressure in the reservoir 92 has fallen to a sufficiently low level—the controllable isolating valve 163 can be transferred to a completely open state, as shown, for example, by signal region 190.3 in FIG. 7. In signal region 190.3, the current signal at least reaches a holding current which is sufficient to hold the controllable isolating valve 163 in a completely open position. Any residual pressure remaining in the reservoir 92 can thus be vented via the series arrangement of the restricting means 62 and the controllable isolating valve 163 with a maximum nominal width of the restricting means 62.

View (B) of FIG. 10 shows the pneumatic system 401 in an operating position which is used to vent the bellows 91 of the pneumatic installation 90 in the form of the air spring installation. For this purpose, the bellows ere opened individually or in groups, according to requirements, although simultaneous opening of all the bellows 91 is avoided. Since the bellows pressure is relatively low in comparison with a reservoir pressure of 13.5 to 18 bar, being in a range of between 5 and 12 bar, there is a reduced risk of an explosive release of air. It is thus fundamentally possible, depending on the design of the pneumatic system 401, for the controllable isolating valve 163 to be moved into a completely open state for the venting process and to remain there. This can be accomplished, for example, by continuous application to the controllable isolating valve 163 of a control signal corresponding to signal regions 190.2 and 190.3 of the PWM control signal 190 in FIG. 7. For example, the controllable isolating valve 163 can be switched to an open state by applying a control signal of signal region 190.2 of the PWM control signal 190, i.e. a control current 192 reaches the switching current I_(S) and then falls to a holding current with the result that the controllable isolating valve 163 is switched to a completely open state and remains there. As an alternative, it is also possible to choose a procedure similar to that described with reference to view (A) of FIG. 10. However, a possibly lower clock rate of a control state change can be chosen for a first phase, described there, of a venting process, i.e. for an initial high pressure peak when the bellows 91 are vented, as compared with a relatively high clock rate of a control state change when the reservoir 92 is vented.

FIG. 11 and FIG. 12 show an expansion of the solenoid valve arrangement 80 shown in FIG. 1 to include a solenoid valve arrangement 800, 800′, which has a vent valve 73 and an isolating valve arrangement 631 and 632 respectively, although all of these—at least the controllable isolating valve 81 and the controllable vent valve 73—are set up to be controlled by means of a control signal 190 which is common to all of them. The common control signal is supplied by the same ECU for all of them.

More specifically, FIG. 11 shows—as part of a further developed variant of the invention—a further embodiment of a pneumatic system 501 with a compressed air supply installation 25 and a pneumatic installation 901, which is shown without a pressure sensor 98 in the present case. A pressure sensor 98 can be fitted for the pneumatic installation 901, as in the pneumatic installations 90 of FIGS. 9A, B, C or as in the pneumatic installation 90 of FIG. 9D for example, i.e. either on the gallery line 95 or on the compressed air reservoir 92. For the compressed air supply installation 25, attention is drawn in principle to the description of FIG. 1. For pneumatic installation 901, an isolating valve arrangement 631 in accordance with the developed variant of the invention is provided in the present case, said arrangement being formed by the isolating valve 63 and a reservoir solenoid valve 94 arranged ahead of the reservoir 92. In the present case, the isolating valve arrangement 631 in accordance with the further variant of the invention is formed with three ports X, Y, Z by means of a first directional control valve, here in the form of a 2/2-way valve—also referred to below as a primary valve—and of a second directional control valve, here in the form of a 2/2-way valve—also referred to below as a secondary valve. The first directional control valve is formed by the isolating valve 63 and the second directional control valve is formed by the reservoir solenoid valve 94. The reservoir 92 is connected via the reservoir branch line 99.2 to port X formed on the first directional control valve. The compressed air port 2 of the compressed air supply installation 25 is connected to port Y, formed on the second directional control valve, via the further pneumatic line 96. The gallery line 95 of the pneumatic installation 901 is connected to the third port Z formed between the first and the second directional control valve. It is thus possible to switch the compressed air port 2, the compressed air reservoir 92 and the gallery line 95 by means of a single isolating valve arrangement 631 using the isolating valve arrangement 631 formed by means of the two directional control valves—i.e. the isolating valve 63 and the reservoir solenoid valve 94—and having three ports X, Y, Z. The embodiment of a PWM control signal 190 which has been described in respect of clocking of an isolating valve 163 can also be implemented unmodified for the isolating valve 63 and/or reservoir solenoid valve 94 in the context of isolating valve arrangement 631.

In the present case, the vent valve 73, the isolating valve 63 and the reservoir solenoid valve 94 are formed as separate 2/2-way valves. Once again, the reservoir solenoid valve 94 is implemented as part of a valve block 97 having five valves—i.e. as a sequence of five 2/2-way valves—together with the gallery line 95. The second directional control valve in the form of the isolating valve 63 is arranged in the further pneumatic line 96 leading to the compressed air port 2. In the embodiment shown here, the second directional control valve in the form of the isolating valve 63 is to be assigned to the compressed air supply installation 25. However, it is not necessary in the present case for the isolating valve 63 to be arranged in the main pneumatic line 60 between compressed air feed port 52 and compressed air port 2, as is the case in the compressed air supply installation 11 of FIG. 1. In principle, therefore, compressed air supply installation 25 can be implemented without the isolating valve 63, and hence the isolating valve 63 is formed separately from compressed air supply installation 25 and separately from the valve block 97.

Moreover, in contrast to the compressed air supply installation 11 of FIG. 1, separate control lines 83, 84.1 and 84.2 are provided for each of the directional control valves in the compressed air supply installation 25 of FIG. 11—i.e. for the vent valve 73, the isolating valve 63 and the reservoir solenoid valve 94 ahead of the reservoir 92. The directional control valves can therefore be controlled separately—although by means of a vehicle controller common to all of them or a control module assigned to the vehicle controller ECU.

FIG. 12 shows a pneumatic system 502 which is of substantially similar construction to pneumatic system 501, in particular having the same compressed air supply installation 25. In contrast, however, in the present case a modified pneumatic installation 902 is provided, in which the isolating valve arrangement 632 is formed by a unit comprising two 2/2-way valves—namely a primary valve I and a secondary valve II. The primary valve I and the secondary valve can advantageously be implemented as part of a double armature solenoid valve, which is connected to the ECU by a single control line 84. In contrast to the embodiments in FIG. 2A and FIG. 2B, in which an isolating valve 63′, 63″ is formed as a modular unit with a vent valve 73′, 73″ to give a double armature solenoid valve with a common control line 83′, 83″, a separate vent valve 73 is provided in the compressed air supply installation 25 in the present case. In contrast, the overall situation is rather that a previously provided isolating valve 63′, 63″—here acting as secondary valve II—together with a previously provided reservoir solenoid valve 94—here acting as primary valve I—is provided as part of a modular unit of a double armature solenoid valve of the isolating valve arrangement 632. In the present case, it is particularly advantageous to implement the isolating valve arrangement 632 as part of the valve block 97, together with the gallery line 95. Once again, the double armature solenoid valve of the isolating valve arrangement 632 according to the further variant of the invention, which has three ports X, Y, Z, also allows joint switching of the compressed air port 2, of the compressed air reservoir 22 and of the gallery line 95 by means of the single isolating valve arrangement 632.

In summary, the invention relates to a compressed air supply installation 11, 21, 22, 23, 24, 25, 30, 41 for operating a pneumatic installation 90, 901, 902, in particular an air spring installation on a vehicle, having:

-   -   a compressed air feed 1,     -   a first pneumatic connection between the compressed air feed 1         and the pneumatic installation 90, 901, 902, which has an air         drier 61, a restricting means 62 and at least one controllable         isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163,     -   a second pneumatic connection, which is connected pneumatically         to the first pneumatic connection and to a vent port 3 leading         to the environment and has at least one controllable vent valve         73, 73′, 73″, 73′″, 73 ^(IV), 173. According to the invention,         provision is made here for the at least one controllable         isolating valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 and the         restricting means 62 to form a series arrangement in the first         pneumatic connection, such that, in a through-flow mode, the at         least one controllable isolating valve 63, 63′, 63″, 63′″, 63         ^(IV), 163 can be switched to an open state and, in an isolating         mode, can be switched to a closed state, wherein, in the closed         state, the first pneumatic connection is bidirectionally and         completely closed and the at least one controllable isolating         valve 63, 63′, 63″, 63′″, 63 ^(IV), 163 can be switched over in         a through-flow mode between a first control state assigned to a         closed state and a second control state assigned to an open         state.

LIST OF REFERENCE SIGNS (PART OF THE DESCRIPTION)

0 air feed

1 compressed air feed

2 compressed air port

3 vent port

11, 21, 22, 23, 24, 25, 30, 41 compressed air supply installation

31 first region

32 second region

33 third region

34 drying canister

51 air compressor

52 compressed air feed port

60 main pneumatic line

61 air drier

62 first restrictor/restricting means

63, 63′, 63″, 63′″, 63 ^(IV), 163 controllable isolating valve

631, 632 isolating valve arrangement

70 vent line

71 nonreturn valve

72 second restrictor

73, 73′, 73″, 73′″, 73 ^(IV), 173 vent valve

74 filter

80, 80′, 80″, 80′″, 80 ^(IV), 180, 800, 800′ solenoid valve arrangement

81, 81′, 81″ first coil

82 second coil

83, 83′, 83″, 83′″, 83 ^(IV), 183, 84.1, 84.2 control line

90, 901, 902 pneumatic installation

91 bellows

92 reservoir

93 bellows solenoid valve ahead of bellows 91

94 reservoir solenoid valve ahead of reservoir 92

95 gallery line

96 pneumatic line

97 valve block

98 pressure sensor

99 sensor branch line

99.1 bellows branch line

99.2 reservoir branch line

101, 201, 202, 203, 204, 300, 401, 501, 502 pneumatic system

160 branch line leading off from the main pneumatic line

170 further branch line

175 control valve

190 PWM control signal

190.1 first signal region

190.2 second signal region

190.3 third signal region

191 voltage signal

192 current signal

A, B, C housing part

D seal

E0 air feed interface

E1 compressed air feed interface

E2 compressed air supply interface

E3 vent interface

F spring

G recess

I_(H) holding current

I_(R) reset current

I_(S) switching current

M motor

MVA solenoid valve arrangement

P venting flow

P supply flow

S control interface

SA current amplitude

SA₁ first current amplitude, switching point

SA₂ second current amplitude, switching point

SA₃ third current amplitude, switching point

SA₄ fourth current amplitude, switching point

T cover

W wall

t time characteristic

t₁ pulse width

t₂ interpulse width

t₃ pulse width

t₄ interpulse width

t₅ pulse width

t₆ interpulse width

t_(R) time

t_(S) time

X_(ES) detail

ES equivalent circuit diagram

U control state change

X, Y, Z port

I primary valve

II secondary valve

Ia first sealing element

IIa second sealing element

Ib primary armature

Iib secondary armature

Ic, Iic valve spring

Id, Iid valve seat

III coil former

(i), (ii) first, second control state

N_(eff) effective nominal width 

1. A compressed air supply installation (11, 21, 22, 23, 24, 25, 30, 41) for operating a pneumatic installation (90, 901, 902), in particular an air spring installation on a vehicle, having: a compressed air feed (1), a main pneumatic line (60) between the compressed air feed (1) and the pneumatic installation (90, 901, 902), which has an air drier (61), a restricting means (62) and at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163), a vent line (70), which is connected pneumatically to the main pneumatic line (60) and to a vent port (3) leading to the environment and has at least one controllable vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173), characterized in that, in an isolating mode, the at least one controllable isolating valve (63, 63′, 63″, 63′″, 83 ^(IV), 163) can be switched into a closed state and forms a series arrangement in the main pneumatic line (60) with the restricting means (62), such that the main pneumatic line (60) is bidirectionally and completely closed in the isolating mode, and the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and the at least one controllable vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) are set up to be controlled by means of a control signal (190) common to both.
 2. The compressed air supply installation as claimed in claim 1, characterized in that the main pneumatic line (60) runs as far as a compressed air port (2) leading to the pneumatic installation (90), wherein, in a closed state of the controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163), the main pneumatic line (60) between the air drier (61) and the compressed air port (2) is bidirectionally and completely closed.
 3. The compressed air supply installation as claimed in claim 1 or 2, characterized in that the controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) is formed with a first coil (81) and the controllable vent valve (73 ,73′, 73″, 73′″, 73 ^(IV), 173) is formed with a second coil (82) and, in particular, the first coil and the second coil are formed with a single coil former (III) common to both coils (81′, 81″).
 4. The compressed air supply installation as claimed in one of claims 1 to 3, characterized in that, in a through-flow mode, there can be a switch to an open state, in which the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) can be switched over by means of the control signal (190) between a first (i) control state, which is assigned to a closed state, and a second (ii) control state, which is assigned to an open state.
 5. The compressed air supply installation as claimed in one of claims 1 to 4, characterized in that a through-flow quantity for the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or the at least one controllable vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) can be subjected to closed-loop and/or open-loop control in the through-flow mode by means of the control signal (190).
 6. The compressed air supply installation as claimed in one of claims 1 to 5, characterized in that a first control state (i) and/or a second control state (ii) of the at least one isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or of the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) can be adjusted in a variable manner by means of the control signal (190), in particular an operating state can be adjusted continuously between the first and the second control state (i, ii).
 7. The compressed air supply installation as claimed in one of claims 1 to 6, characterized in that, in a through-flow mode, the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) can be switched over backward and forward by means of the control signal (190) between a first and a second control state (i, ii) at a clock rate of a control state change (U).
 8. The compressed air supply installation as claimed in claim 7, characterized in that a clock rate of a control state change (U) is between 4 and 20 Hz.
 9. The compressed air supply installation as claimed in one of claims 1 to 8, characterized in that the control signal (190) is a PWM control signal, in particular in the form of a current and/or voltage signal.
 10. The compressed air supply installation as claimed in one of claims 1 to 9, characterized in that, in the through-flow mode, the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) can be switched over by means of the control signal (190) between a first and a second control state (i, ii) in such a way that an effective nominal width (N_(eff)) of the series arrangement comprising the restricting means (62) and the controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) is below an actual nominal width of the restricting means (62).
 11. The compressed air supply installation as claimed in one of claims 1 to 10, characterized in that the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173), as a directly switched valve, is part of a solenoid valve arrangement (80, 80′, 80″, 80′″, 80 ^(IV), 180, 800, 800′) for directly switching a compressed air volume.
 12. The compressed air supply installation as claimed in one of claims 1 to 10, characterized in that the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173), as an indirectly switched relay valve, is designed as part of a solenoid valve arrangement (MVA, 80, 80′, 80″, 80′″, 80 ^(IV), 180) for indirectly switching a compressed air volume, wherein the solenoid valve arrangement (80, 80′, 80″, 80′″, 80 ^(IV), 180, 800, 800′) has a control valve (175) for controlling the relay valve, which control valve is subjected to a pressure of the main pneumatic line (60), in particular the total pressure.
 13. The compressed air supply installation as claimed in one of claims 1 to 12, characterized in that a reservoir solenoid valve (94), as a further controllable isolating valve, is formed with a further coil, and the controllable isolating valve (63) is formed with a first coil, wherein the first coil (I) and the further coil are formed with a single coil former common to both coils.
 14. A pneumatic system (101, 201, 202, 203, 204, 300, 401, 501, 502) having the compressed air supply installation (11, 21, 22, 23, 24, 30, 41) as claimed in one of the preceding claims and a pneumatic installation (90, 901, 902), in particular an air spring installation on a vehicle.
 15. A method for operating a pneumatic installation (90, 901, 902), in particular an air spring installation on a vehicle, having a compressed air supply installation (11, 21, 22, 23, 24, 30, 41) as claimed in one of claims 1 to 13, in which, in an isolating mode, the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) is switched into a closed state and forms a series arrangement in the main pneumatic line (60) with the restricting means (62), such that said main pneumatic line is bidirectionally and completely closed in the isolating mode, and the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and the at least one controllable vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) are controlled by means of a control signal (190) common to both.
 16. The method as claimed in claim 15, characterized in that the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) are switched over backward and forward between a first and a second control state (i, ii) at a clock rate of a control state change (U).
 17. The method as claimed in claim 16, characterized in that the at least one controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and/or the at least one vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) are switched over backward and forward between a first and a second control state (i, ii) by means of a control signal, preferably by means of a PWM control signal, in particular in the form of a current and/or voltage signal, at a clock rate of a control state change (U) of between 4 Hz and 20 Hz.
 18. The method as claimed in one of claims 15 to 17, characterized in that, in the isolating mode, the controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) is closed when deenergized.
 19. The method as claimed in claim 18, characterized in that, in the isolating mode, the controllable isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) and the vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) are closed when deenergized, and the vent valve (73, 73′, 73″, 73′″, 73 ^(IV), 173) makes a transition to a through-flow mode only after the isolating valve (63, 63′, 63″, 63′″, 63 ^(IV), 163) has been switched to the open state. 